Handling Errors and Job Lifecycles in Rails 7.1: A Guide to retry_on, discard_on, and after_discard

Mastering ActiveJob Error Handling in Rails 7.1

Ruby on Rails 7.1 has brought some essential improvements to ActiveJob that make error handling and job lifecycle management easier and more flexible. Here’s a breakdown of three significant features: after_discard, discard_on, and retry_on, complete with examples for anyone looking to get up to speed.

1. after_discard Hook

The new after_discard callback in Rails 7.1 provides an opportunity to execute custom logic when a job is discarded. It’s particularly useful when you need to clean up resources or notify relevant parties about a failure.

Example:

class MyJob < ApplicationJob
  discard_on CustomError

  after_discard do |job|
    Rails.logger.info "Job #{job.job_id} was discarded."
    # Custom logic, e.g., notifying an admin
  end

  def perform
    # Job logic that might raise a CustomError
  end
end        

In this snippet, if CustomError occurs and the job is discarded, the after_discard callback will log the event or execute any custom actions you define.

2. discard_on for Handling Irrecoverable Errors

discard_on allows you to specify exceptions for which jobs should be discarded rather than retried. This feature is a lifesaver when some errors are irrecoverable, and retrying would be wasteful or harmful.

Example:

class ExampleJob < ApplicationJob
  discard_on ActiveRecord::RecordNotFound

  def perform(record_id)
    record = MyModel.find(record_id)
    # Perform work on the record
  end
end        

Here, if the job tries to find a record that doesn’t exist, it is gracefully discarded, avoiding unnecessary retries and resource use.

3. retry_on for Recoverable Errors

Conversely, retry_on helps handle temporary failures that you expect might resolve over time, like network issues. You can customize retry delays and limits.

Example:

class RetryJob < ApplicationJob
  retry_on Net::OpenTimeout, wait: 5.seconds, attempts: 3

  def perform
    # Logic that might encounter a timeout
  end
end        

In this case, if a Net::OpenTimeout occurs, the job will retry up to three times with a 5-second delay between attempts.

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